A drive device of this type is disclosed in DE-A-25 17 134. On a shaft mounted rotatably about its axis, which shaft is acted upon eccentrically by an energy store configured as a tension spring, there is seated in rotationally secure arrangement a cam disk, the curve path of which exhibits a first section having a radius which steadily increases as the azimuth increases counter to the direction of rotation of the shaft. The rear end of the first section, in the direction of rotation, is directly adjoined by a second section, running roughly in the radial direction, of abruptly decreasing radius, which second section is adjoined, counter to the direction of rotation, by a third section, which runs up to the start of the first section and exhibits a radius roughly corresponding to the radius at the start of the first section.
A control shaft connected to the movable contact of the power switch is disposed parallel to the shaft and, seated on the shaft, in rotationally secure arrangement, there is a disk from which there eccentrically protrudes, relative to the axis of the control shaft, a pin-like follow-up member. In addition, the shaft is connected to a disconnecting spring. On its periphery, the disk exhibits a latch recess which is designed to interact with a disconnecting pawl of a ratchet device.
For the tensioning of the connecting spring, the shaft is rotated out, in the direction of rotation, to above the unstable dead center and is held there supported by a connecting pawl. For the switching-on of the switch, the connecting pawl is tripped, whereby the shaft, due to the force of the connecting spring, starts to rotate in the direction of rotation. The cam disk hereupon runs with its first section onto the follow-up member and, upon further rotation, pivots the control shaft out of its switch-off setting into the switch-on setting and by a measure of one overtravel beyond this. This overtravel is generally necessary to ensure the latching of the ratchet device. As soon as the first section of the curve path runs off from the follow-up member, the disconnecting spring accelerates the control shaft until it is in contact with the disconnecting pawl. The ratchet device has thus not only to support the force of the disconnecting spring, but also to absorb the additional impact stress resulting from the impacting upon the disconnecting pawl. For the activation and simultaneous tensioning of the disconnecting spring, the shaft rotates by about 180.degree., the surplus energy being recuperated into the connecting spring by rotation beyond the stable dead center position.
A further drive device of the generic type is disclosed in CH-A-498 480. A cam disk, which can be rotated by means of connecting springs, for switching on the switch, respectively by 360.degree. in the direction of rotation exhibits a curve path having a first and a second section. The radius of the first section increases steadily in a spiral, as the azimuth increases counter to the direction of rotation, and sweeps an angle of almost 360.degree.. Extending between the end of the first section of largest radius and its start there is the abruptly down-sloping second section, which extends in the radial direction. Interacting with the cam disk is a follow-up member, configured as a roller, which is mounted at the one end of a twin-armed lever, the other end of which is designed to interact with a ratchet device and which is connected to the movable contact of the power switch and a disconnecting spring. As a result of the impulsive rotation of the cam disk by 360.degree., the lever is moved out of its switch-off setting from the first section, as the switch is simultaneously switched on and the disconnecting spring tensioned, into the switch-on setting and beyond this. If the first section runs off from the follow-up member, the disconnecting spring accelerates the lever in the opposite direction until the latter is in contact with the ratchet device. Here too, the ratchet device has to absorb, in addition to the force of the disconnecting spring, the dynamic force resulting from the impacting of the lever, also.
In both the known drive devices, the ratchet device must therefore be dimensioned in correspondingly large size. This requires a considerable amount of space and leads to large masses, which have to be moved for unlatching purposes. The movement of these large masses calls, in turn, for high drive powers for the ratchet device or it results in a slow unlatching procedure.
A drive device exhibiting a cam disk, which drive device possesses, in relation to the two aforementioned drive devices, a different structure and a different working method, is disclosed in EP-A-0 150 756.
A roller-like follow-up member, which interacts with the curve path of the cam disk, is disposed on a lever which is actively connected to the connecting spring. The curve path of the cam disk, which cam disk can be driven by a motor or by hand in the direction of rotation, exhibits a first section of a radius which steadily increases as the azimuth increases counter to the direction of rotation. Counter to the direction of rotation, this first section is adjoined by a section of a radius which slowly becomes steadily smaller as the azimuth increases, which section is adjoined, for its part, by a second section running essentially in the radial direction, which is followed at the inner end by the first section. When the connecting spring is relaxed, the follow-up member bears against the start of the first section. By the slow rotation of the cam disk in the direction of rotation by somewhat less than 360.degree. up to the end of the first section, the connecting spring is tensioned. Upon the interaction of the follow-up member with the subsequent section of slowly decreasing radius, the connecting spring has the effect of driving the cam disk in the direction of rotation. The cam disk, which is now decoupled from the motor, is prevented however, by means of a ratchet device, from further rotating. For the switching-on of the power switch connected to the drive device, the ratchet device is excited in order to release the cam disk. The latter, under the force of the connecting spring acting via the lever, starts to rotate and the follow-up member makes its way onto the abruptly down-sloping second section, so that there is now no longer any counter-force exerted by the cam disk against the action of the connecting spring. Under the force of the connecting spring, the follow-up member is now suddenly accelerated as the switch is simultaneously switched on and a disconnecting spring is tensioned. In this particular drive device, the cam disk is used to tension the connecting spring and additionally acts as a ratchet transmission. In this known drive device, furthermore, it is necessary after the switching-on, by means of a special device, to decouple the switch and disconnecting spring from the connecting spring.